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Question: Voltage fluctiating at irregular times

It has been going on over a year. at first, the voltage would rise up to 14(?) and then drop to 10.5(?). It only happened once in a while. I replaced my battery and the symptoms seemed to go away for a couple of weeks. It came back, but would only happen at highway speeds on long trips every once in a while. Lately, it happens often. The volts jump up and down. My a/c blower fluctuates speeds, headlights flash. I ve tried to turn off every auxilary motor/lights to pinpoint the cause with no luck. This happens night or day. Just recently, my a/c blower started acting up as well. Sometimes it will not turn on. When it does, it will not go to high. Also, when I turn the truck off, the blower continues to run even after the key is out and the doors are opened/closed. im assuming this may be a byproduct of the original voltage problem. Could it be my alternator/regulator? I do not have and trouble codes or dummy lights on.